Myofascial pain is associated with the formation of pain trigger points or defined areas within a muscle block that exhibit tenderness and abnormal tightness. Acupuncture is an alternative approach to releasing trigger points, thus relieving pain and the associated muscle tension in many cases. Although this therapeutic approach is efficacious, there is little scientific evidence to support the clinical relief shown following treatment. Our group designed and developed an acupuncture needle with a hollow stem through which a twin tube microdialyzer could be inserted. The exterior bore of the needle was 28 - 30 gauge stainless surgical steel, with one end beveled into a blunt, non-cutting tip by micro-polishing. A 100,000 m.w. cutoff dialyzer membrane was attached to a 30-gauge poly-ether-ether-ketone (PEEK) biocompatible tubing and a 33-gauge PEEK tubing inserted into the first tube, thus forming an inlet and return flow-path terminating in the dialyzer membrane. This apparatus was fixed inside the stainless steel tubing so that the dialyzer surface was flush with the hole in the needle tip. A handle was fixed to the other end of the needle, allowing the operator to manipulate the needle in a similar manner to a solid acupuncture needle. Three groups of patients, two with various degrees of muscle pain and tension, plus controls, were recruited to the study. The acupuncture needle was inserted in the shoulder muscle by a skilled acupuncture specialist and samples taken, via microdialysis, from the needle tip. The samples were collected and analyzed for a variety of analytes, such as blood gases, cytokines, hormones, neuropeptides, and electrolytes by the Ultramicro Immunodiagnostics group, using established techniques (capillary electrophoresis, capillary electrochromatography, micro-ion selective electrochemistry and micro gas sensors). This project is recruiting subjects under an IRB-approved protocol and has completed the first phase of the protocol. There were clear differences between the three test groups, with the normal group demonstrating little to no variation over the entire treatment time. The latent group demonstrated moderate concentrations of pain-associated neuropeptides as well as inflammatory cytokines. These concentrations returned to normal during the elicitation of a twitch reaction or firing of the trigger point. Additionally, the subjects unanimously stated that they felt pain relief and loss of muscle discomfort following treatment. The severe group demonstrated relatively high, localized concentrations of pain-associated neuropeptides and inflammatory cytokines, which became reduced but not completely removed during the treatment. Although some pain relief was noted, the majority of the subjects continued to feel some degree of muscle tension and light pain. Further studies are in progress to examine the effects of repeat treatments and chemical changes in these subjects as compared to normals. Studies are ongoing to determine if the biochemical and immunological changes seen during dry-needling of active trigger points are unique for the trigger point itself. A series of subjects was tested in which the needle was inserted not only into the actual trigger point itself but also into an unrelated muscle, i.e., the calf muscle. These studies are still underway, but early analysis suggests that patients with active trigger points have a generally higher level of inflammatory biomarkers independent of the muscle sampled. Additionally, plans are underway to investigate the potential of the needle to deliver medications via the microdialysis tip to defined anatomical areas, especially muscle trigger points.